Intensifying and fluorescent screen



INTENSIFYING AND FLUORESCENT SCREEN Original Filed March 8, 1954 YRessueil Sept. 2:6, 1939 UNITED STATES PATENT OFFICE INTENSIFYING ANDJ FLUoREscENT SCREEN John Eggert and Fritz Luft, Leipzig, Germany, assignors, by mesne assignments, to Agfa Ansco Corporation, Binghamton, N. Y., a corporation of Delaware Claims.

Our present invention relates to an intensifying or fluorescent screen for X-ray work.

One of its objects is an improved screen of this kind. Further objects will be seen from the detailed specification following hereafter.

Many intensifying and uorescent screens for use in X-ray work have the drawback to show phosphorescence, that is to say, the screens not only emit the desired fluorescent radiation -during the diagnostic exposure, but also produce after exposure a phosphorescent light, at the places previously struck by the X-rays so that on the screens the successively produced phosphorescent and fluorescent pictures become mixed, a fact which may render difficult the interpretation of the inspected or photographed picture. As known, it is very difficult to free the luminescent substances used in the manufacture of intensifying screens and fluorescent screens for X-ray work from substances that phosphoresce when struck by X-rays.

This phosphorescent light frequently has a color different from that of the fluorescent light. By the invention the detrimental effect caused by vthe phosphorescent substances contained in the fluorescent layer may be eliminated by coating the intensifying screen or the uorescent screen with a lter layer which transmits the fluorescent light completely or in greater part, but absorbs the phosphorescent rays. By this expedient the manufacture of intensifying and fluorescent screens for X-ray work is considerably cheapened and improved, because on the one hand the complicated process of removing the phosphorescent admixtures from the fluorescent substances is rendered unnecessary and on the other hand there (Cl. Z50-80) ing agent carrying the fluorescent substance instead of being incorporated in a special filter layer.

Furthermore, substances are known, such as zinc sulde and sulfides of the alkaline earths, which iiuoresce and phosphoresce when struck by X-rays or by daylight. If such substances are used for the manufacture of intensifying screens, these screens must, of course, always be protected from daylight, thus causing much. trouble in X-ray Work,

Now, according to Stokes law, these luminesf cent rays always have a greater wave length than the exciting primary rays. By providing fluorescent screens with a lter (in the way above referred to, i. e., applying a filter layer by casting or dyeing the layer throughout its thickness) which absorbs only the exciting light, and transmits the luminescent rays completely or in greater part, the risk that such a screen be excited in daylight is greatly diminished, Without the excita'bility by X-rays being reduced or the emission of the fluorescent rays being materially hindered. With a screen protected in this manner, therefore, the X-ray work may be done almost irrespective of any previous exposure to daylight.

In the following table there are given some materials which are used for manufacturing intensifying or fluorescent screens and materials which they may contain as impurity. There is further indicated the fluorescent and phosphorescent light emanated by these materials and the lter dye to be used for absorbing the phosphorescent light.

Main constituent Impurity Corlgsrclfnglo Cllgggo Filter dye ZnS activated with Mn Dark blue." Orange Toluidine blue (cf. Schultz Farbstoitabellen Ag 7th editlcn No. 1041) or Crystal Violet (hexamethylpararosaniline). ZnS activated with Gu do Green Rose bengale (ci. Schultz Farbstofitabellen Ag. 'I th edition No. 889) ZnS activated with Mn.-." Orange yeldo Orange 2 (cf. Schultz Farbstoltabellen 7th Cd. 10W. edition No. 189). OaWO4 ZnS ac Blue do Rose bengale (cf. Schultz Farbstofitabellen tivated 7th edition No. 889). w i t h Mn.

is a Wide choice of uorescent substances since those which give fluorescent and also phosphorescent substances can be used. If required, the filter dyestuff may be added directly to the bind- The following examples illustrate the invention:

Example 1.-An intensifying screen for X-ray work consists of a support, for instance stiff paper, and a iluorescent layer, containing as a fluorescent substance, Zinc sulfide activated with silver. This layer is coated with another layer containing as a filter dyestuff hexamethylpararosaniline in gelatin as a binding agent. If the zinc sulde activated with silver and fluorescing in a blue color, contains as usual traces of copper, the screen will phosphoresce in a green light, Which is absorbed by the yiilter layercontaining hexamethylpararosaniline. The blue iiuorescent light penetrates the iilter layer unweakened.

Example 2.-An intensifying screen containing as an active substance zinc sulfide activated with copper is coated with a green iilter layer of gelatin dyed with Tartrazine (cf. Schultz Farbstoitabellen, '7th edition, No. 737), and Patent Blue (cf. Schultz Farbstofftabellen, 7th edition, No. S26). This filter layer prevents the screen from being excited by daylight by absorbing theblue rays exciting phosphorescence. On the contrary, X-rays Whichare not absorbed by such a lter excite a Yfluorescent radiation. The yellowish- .green fluorescent light produced is transmitted by the iilter layer.

Our invention-is illustrated in the accompanydrawing in which Fig. 1 shows a modification in which thelayer containing the fluorescent material is provided with a filter layer for absorbing phosphorescent light and Fig. 2 shows a modication in which the layer containing the iiuorescent material is colored throughout by a dye absorbing phosphorescent light.

What We claim is:

1. An intensifying or fiuorescent screen for X- ray work which comprises a layer containing a fluorescent material and a filter layer containing a dye permeable to the fluorescent light produced on excitation of said fluorescent material ,and absorbing the phosphorescent light.

2. An intensifying or fluorescent screen for X- ray Work which comprises in its active layers a fluorescent material and a dye permeable t fluorescent light produced on excitation of said uorescent material and absorbing the phosphorescent light` 3. An intensifying or fluorescent screen for X- ray Work Which comp-rises uniformly distributed in a binding agent a iiuorescent material and a dye permeable to fluorescent light produced on excitation of said fluorescent material and absorbing the phosphorescent light.

4. An intensifying or fluorescent screen for X- ray Work which comprises a layer containing zinc sulfide activated with silver and coated on this layer with a layer of gelatin dyed With hexamethylpararosaniline` 5. An intensifying screen, comprising active uorescent material and an associated medium having color value adapted totransmit fluorescent light produced on excitation of said fluorescent material and to absorb a substantial part of the afterglow/fof said material.

6. In an intensifying screen for use in X-ray examination Aand including an active luminescent material, a 4light -lter of spectral composition adapted to transmit fluorescent light produced on excitation-of said luminescent material and to absorb a substantial part of the afterglow of said. material.

substantially -.opaque to lightof said ,spectraldistribution and substantially transparent `to alight of a lcolor `falling Within the remainder `of the spectrum, f and.- assocating such :selected vmedium with the ,said luminescent material ,in a .position relative thereto in order to absorb the phospho- ,rescent luminescence of said material.

A8. The method of .suppressing ,the phosphorescence of luminescentmaterial, comprising the vsteps of determining the Aspectral v.distribution of said Yphosphoressentie; selecting a dye having a color'value `capable ofrsubstantially absorbinglthe light of s aidspectraldistribution, andtransmitting substantially `unhinfilelied the ,fluorescent light of the -saidluminescent material; and yassociating vsuch selected dye with the said luminescent material in V.a .position relative -thereto in order to absorb the Vphosphcrescent luminescence of said material.

9. Intensifying means for use in radiography comprising a layer containinga iiuorescentmaterial, and a material associated `Withsaid layer capable of absorbingnphosphorescent light Vfrom said material While being permeable to fluorescent light from said material.

10. Intensifying'means for use in radiography comprising a layer containing a fluorescent material, and a-dye associated with said layer capable of absorbing phosphorescentlight from said material While .being permeable to fluorescent light from said material.

JOHN EGGERT. FRITZ VLUFI- 

